1. Field of the Invention
The present invention relates to a material flow control for a spraying apparatus and, more particularly, for an airless spray gun for atomizing liquids having a pump piston and pump drive arrangement including a coil and a swinging armature.
2. Description of the Prior Art
Airless spray guns conventionally employ various techniques to limit the flow of liquid out of the spray tip. Well-known devices accomplish this by varying the output of the A-C motor or by limiting the oscillation and stroke length of the armature which drives the piston that will pump the liquid. Various electronic suppression control systems, such as disclosed in U.S. Pat. No. 4,705,995, and mechanical devices, such as disclosed in U.S. Pat. No, 4,744,516, successfully change the stroke length and rate of the swinging armature. However, these known spray guns suffer from inferior atomization quality because they rely on reduction of input power to reduce the flow. Reduction of input power decreases pressure at the spray nozzle which will make it impossible to provide a fine spray. As a result, coarse atomization will occur. Degradation of overall spray performance is attributable to this decrease in pressure at the atomizer.
In none of the known airless spray guns is it possible to control the flow of liquid while maintaining high atomization quality and simplifying the entire control system. No conventional airless spray guns maintain maximum input power while adjusting flow rates, nor do they provide fine atomization at lower flow rates.